Field of the Disclosure
Embodiments of the present disclosure generally relate to data storage and computer memory systems, and more particularly to metal-oxide-semiconductor (MOS) select transistors formed in a vertical orientation.
Description of the Related Art
Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. Many types of memory exist including random access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory; however, each is useful only for 2-D memory fabrication or they are serially connected and, as such, must operate similarly to NAND flash strings.
Flash memory devices have developed into a common source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and lower power consumption. Common uses of flash memory include personal computers, personal digital assistants (PDAs), digital cameras, and cellular phones. The performance of flash memory devices needs to increase as the performance of computer systems increase.
Amorphous silicon (a-Si) based thin film transistors (TFT) have been used to improve transistor performance; however, these transistors have undesirable short channel effects and randomness in device characteristics. This is largely due to the randomness of in polysilicon grain size and grain boundaries that exist in TFT devices.
Silicon carbide (SiC) substrates have been used in power devices due to the higher bandgap over silicon. Wide bandgap materials such as SiC substrates have very low intrinsic carrier concentration and thermal generation scales directly with the intrinsic carrier concentration. Therefore, junction leakage currents in SiC substrate devices are very low. However, SiC substrates suffer numerous problems. For example, wafer sizes in excess of four inches that have high quality and low cost are difficult to achieve. Additionally, the defect densities are unacceptable and the substrates suffer from poor carrier mobility for high speed switching.
Therefore, what is needed in the art is higher performance vertical memory select transistors which maintain area efficiency and increased read and write speed operations in memory cells.